Posted by **killie** on Thursday, April 30, 2009 at 7:01pm.

I am very confused about the concepts of..

sin è = sin(180 - è)

sin (180 + è)= -sinè

tan (180 - è) = -tanè

and how the final answer was found in this problem...

Find cos 510:

cos510=cos(540-30)

=-cos30

=-s.r3/2

i don't understand how we went from -cos 30 to -s.r3/2 ?